1. Field of the Invention
The present invention relates to aerial work platforms, and more particularly pertains to a new aerial work platform apparatus and method that are safer and easier to use that foregoing lifts.
2. Description of the Prior Art
Aerial work platforms (AWPs) encompass a variety of different configurations, all designed for the purpose of providing temporary access to elevated areas. Numerous types of lifting mechanisms may be employed for raising and lowering AWPs, including articulated lifts, such as bucket trucks, boom lifts or “cherry pickers,” scissor lifts, and mechanical lifts, such as those employing rack and pinion elements or screw thread elements. Scissor lifts, in contrast to boom lifts, are able to move in only in a vertical direction, because of the scissor mechanism. The scissor mechanism comprises a support with a plurality of pivotally linked, folding elements that criss-cross each other in a substantially X-shaped pattern. The folding support, when in a contracted position, appears as a stack of the plurality of substantially horizontal, elongated elements. A hydraulic cylinder is interposed between an adjacent set of elongated elements such that expansion of the hydraulic cylinder causes the elongated elements to pivot in relation to each other, unstacking the elements and extending the structure, and as a result raising the work platform. Lowering of the support is performed by contracting the hydraulic cylinder and as a result the support, so that the elongated elements return to their stacked position, also by pivoting in relation to each other.
Because AWPs are typically used for work of a temporary nature, conventional AWPs include a wheeled chassis having an electric or combustion motor for driving one or more of the wheels. Transporting the platforms over long distances generally requires trailering of the apparatus, as self-motivated AWPs are not suited for highway use. Conversely, AWPs mounted directly on a trailer chassis may be moved by attaching the trailer chassis to a vehicle. Long distance transportation of a trailer chassis mounted AWP is possible where the device has wheels intended to rotate at highway speeds. In order to increase maneuverability, trailer chassis mounted AWPs typically employ a single axle, though use of a multiple axles is possible. Regardless of whether a single axle or a multiple axle is employed, the nature of AWPs typically requires some kind of stabilization apparatus to prevent lateral movement from causing a partially- or fully-extended lift to overturn. In their fully extended position, the distance between the work platform and trailer chassis substantially exceeds the horizontal dimensions of the portion of the trailer chassis in contact with the ground. Because the ratio of the height of the unit to the width of its base is high, the lateral stability of the AWP is affected by even relatively small lateral movements of the work platform. This problem is magnified when the trailer is supported by relatively soft highway tires. To overcome the problem of lateral instability, it is known to use a support apparatus to secure or brace the device. The support apparatus may comprise either a securing mechanism, in which the lift is secured to a fixed object, or a bracing mechanism, in which fixed legs connect the chassis of the AWP to the ground in order to increase the effective footprint of the device. The increased footprint resulting from the use of a support apparatus decreases the AWP's lateral instability, increasing the amount of lateral force necessary to overturn the lift apparatus.
A number of existing methods for bracing an AWP to bolster lateral stability have been used. In one method of bracing an AWP, outriggers are provided which extend from the lift's frame. Mounted on an outer end of these outriggers is a manually operated, screw-type leveling jack. In use, an operator applies rotary motion to the handle of the screw-type leveling jack, causing a wheel and caster component of the jack to either raise or lower. The operator manually positions the wheel and caster component in a vertical direction so that the wheel engages the ground. By successively adjusting the leveling jacks on each of the four outriggers, an operator can cause the AWP to be completely supported by the outriggers. Furthermore, by continuing to adjust the leveling jacks on the outriggers, an operator levels the machine.
In another method of bracing an AWP, folding outriggers are employed. The outriggers consist of a channel member connected to the base of the AWP through a pivoting mechanism, which allows the outriggers to pivot in the horizontal plane of the base. In their folded position, the outriggers are positioned along the base of the AWP so that the width of the lift is minimized. In their unfolded position, the outriggers are positioned perpendicular to the side of the base on which they are connected, so that the outriggers maximize the width of the lift.
Because proper leveling, bracing and operation of an AWP is necessary to ensure the safety of both the operator and those around the AWP, it is believed that an improved aerial work platform apparatus and method of use is needed.